Method for manufacturing an optical element by bonding a plurality of elements

ABSTRACT

An optical element manufactured by bonding a plurality of elements by hydrolysis product of alcoholate, metal acid ester or metal hydrate colloid, and a method for manufacturing the same are disclosed.

This application is a continuation of application Ser. No. 07/857,122filed Mar. 25, 1992, now abandoned, which is a continuation ofapplication Ser. No. 07/445,125 filed Dec. 4, 1989, now abandoned, whichis a division of application Ser. No. 07/061,551 filed Jun. 15, 1987,now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for manufacturing an opticalelement by using alcoholate as bonding material.

The present invention relates to a method for manufacturing an opticalelement used for a transmissive optical element, particularly an opticalelement used in an ultraviolet range, by using Si-alcoholate as bondingmaterial.

The present invention relates to a method for manufacturing an opticalelement by using a hydrolysis product of at least two metal alcoholatesas bonding material so that a refractive index of a bonding layer may beselected from a wide range (for example 1.45˜2.2).

2. Related Background Art

In the past, balsam, epoxy or ultraviolet ray cured bonding material hasbeen used to bond light transmissive optical elements such as lenses orprisms. Such bonding material, however, does not have a matchingrefractive index with a substrate (optical element), the bonding layeris too thick, or optical design is difficult because a transmissionfactor in an ultraviolet range (200˜400 nm) is low. Thus, the selectionof the substrate is restricted.

For a high energy ultraviolet ray as represented by an Xma laser, thebonding material absorbs the ray. As a result, durability of the bondingmaterial is low and the optical elements cannot be bonded. Accordingly,in the manufacturing process of the optical element. The only way to usean optical contact to bond the optical element. However, in order to getthe optical contact, it is necessary that a surface roughness of abonding surface be very small, for example, 1/100 of a wavelength. Tothis end, the surface of the optical element must be fully polished or athin film must be formed on the optical element. However, when the thinfilm is used, a bonding strength is low, and the polishing is atroublesome work.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method formanufacturing an optical element having a practical sufficiently highbonding strength, by using bonding material which is easily matched witha refractive index of a substrate.

It is another object of the present invention to provide a method formanufacturing an optical element by bonding a plurality of elements,Which optical element is suitable for a light in a wavelength range of200˜400 nm.

In order to achieve the above objects, the present method formanufacturing the optical element is characterized by bonding aplurality of elements by a hydrolysis product of at least one of metalalcoholate, metal acid ester and metal hydroxide colloid.

In accordance with one aspect of the present method for manufacturingthe optical element used for the ultraviolet range, a plurality ofelements are bonded by the hydrolysis product of silicon alcoholate.

In the bonding process by using the hydrolide of silicon alcoholate, ifthe element is made of a material other than fused silica (SiO₂), a SiO₂layer is formed on a bonding surface of the element, and then thebonding process is performed. This process enhances the bondingstrength.

In view of the features described above, the optical elementmanufactured by the present method meets the requirements for thebonding of the optical element used in the light transmissive opticalsystem, that is 1 the bonding strength is practically sufficiently high,2 the refractive index of the bonding material matches with that of thesubstrate, 3 the transmission factor of the bonding layer is high andabsorption and scattering are not substantially included, 4 the bondinglayer is very thin, and 5 the durability (particularly to laser) of thebonding layer is high. This is because the bonding layer of the opticalelement manufactured by the present method is similar to glass usuallyused as the substrate.

Since the metal alcoholate can maintain high precision in its chemicalcomposition and provide homogeneous vitreous material, the opticalcharacteristic of the optical element manufactured is not affected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a bonded lens manufactured by the present method formanufacturing the optical element.

FIG. 2 shows a prism type polarized beam splitter manufactured by thepresent method.

FIG. 3 shows reflection factor characteristics of P polarizationcomponent and S polarization component of the polarized beam splittershown in FIG. 2, for a KrF Xma laser beam.

FIG. 4 shows another prism type polarized beam splitter manufactured bythe present method.

FIGS. 5 and 6 show reflection factor characteristics of P polarizationcomponent and S polarization component of polarized beam splittershaving layer structures shown in Tables 1 and 2.

FIG. 7 shows a flow chart of the method for manufacturing the bondedlens shown in FIG. 1, and

FIG. 8 shows a flow chart of the method for manufacturing the polarizedbeam splitters shown in FIGS. 2 and 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a typical bonded lens (composite lens) comprising fluorite(CaF₂) and synthetic silica (SiO₂). A synthetic silica lens 1 having anegative refractive index and a fluorite lens 2 having a positiverefractive index are bonded by a bonding layer 3. The bonded lens may beused for a light of wavelength range of 200˜400 nm.

In order to manufacture the bonded lens in accordance with the presentinvention, it is necessary to prepare metal alcoholate, preferablySi-alcoholate. Various types of Si-alcoholate may be used. For example,ethyl silicate Si₅ O₄ (OC₂ H₅)₁₂ which is relatively easy to obtain maybe used. Si_(n) O_(n-1) (OR)_(2n+2) (where R is a substituted ornon-substituted hydrocarbon radical, and n is no smaller than one) asrepresented by Si_(n) O_(n-1) (OC₂ H₅)_(2n+2) such as silicontetraethoxide Si(OC₂ H₅)₄, or Si-alcoholate such as R_(n) Si(OR)_(4-n).

When Si-alcoholate is hydrolyzed, it produces SiO₂ which hassubstantially the same refractive index as that of synthesized silicaEnd has bonding ability. In the present embodiment, it is used as thebonding material for the silica glass lens and the fluorite lens.Condition and catalyst for the hydrolysis of Si-alcoholate are notlimited but it may be hydrolyzed in a usual manner.

After the hydrolysis, alcohol or ester solvent residues, such as lowboiling point alcohol or ester (for example, ethyl alcohol or estersulfate, volatizes after the bonding. In order to positively remove it,the assembly may be heated or vacuumed. If there is foreign materialsuch as dust or impurity on the bonding surface, the bonding strength islowered or it may be damaged by the laser. Accordingly, it is necessaryto fully clean the bonding surface before the bonding process and filterthe bonding material to remove the impurities. A clean room ispreferable for a work environment.

In order to bond the silica lens 1 and the fluorite lens 2, thehydrolysis product of Si-alcoholate is coated to the bonding surfaces ofthe lenses. This may be done by a conventional method such as droppingthe hydrolysis product onto the bonding surfaces and bonding themtogether. When it is desired to form a thin bonding layer such as 1 μm,the following method is preferable. The lenses are contacted together,the hydrolysis product of Si-alcoholate is injected into a clearancetherebetween by an injector so that the hydrolysis product is spreadover the entire bonding surfaces of the lenses by a capillarity . Inthis method, in order to spread the hydrolysis product of Si-alcoholateover the bonding surfaces and control the rate of formation of the filmand the film thickness, it is necessary that the hydrolysis product ofSi-alcoholate has an appropriate viscosity. This is attained by solvingthe hydrolysis product of metal alcoholate into a selected solution. Thesolution may be a high boiling point alcohol such as butyl alcohol, orester.

FIG. 7 shows a flow chart of the manufacturing method described above.

A refractive index of the silica lens 1 to the KrF Xma laser (λ=248 nm)is approximately 1.53. The bonding layer 3 of the bonded lens comprisingthe silica lens 1, and the fluorite lens 2 manufactured by the presentmethod is an SiO₂ film having a thickness of 1 μm whose refractive indexto the KrF Xma laser is approximately 1.53.

Accordingly, in the bonded lens shown in FIG. 1, the refractive index ofthe silica lens 1 matches to that of the bonding layer 3 and a bondedlens having a good optical property as the KrF Xma laser lens isprovided.

By heating metal alcoholate after hydrolysis, it changes to an amorphousfilm of a metal oxide having more dehydration and polymerization, andapproaches to the material of the optical element. For example,Si-alcoholate changes to an amorphous film of SiO₂ having deeplypolymerized structure --Si--O--Si--. In the present invention,particularly in the present embodiment, the bonding layer withoutheating exhibits the same optical characteristic as that obtained byheating and practically sufficiently high bonding ability is presented.Therefore, heating is not usually required.

In the present method, the metal alcoholate such as Si-alcoholate whichproduces a compound which exhibits the essentially same refractive indexas that of the optical element to be bonded by the hydrolysis may beused as the bonding material. Other metal alcoholates which can be usedin the present method are Al isopropoxide, Zn propoxide and Tiisopropoxide. In certain cases, the metal alcoholate used as the bondingmaterial may be selected without taking the refractive index of theproduct of the metal alcoholate into account. In this case, the bondinglayer is oxidized and approaches to the material of the optical element.Accordingly, it is better than the balsam or epoxy bonding material fromthe standpoints of 1-5 above.

In the present invention, metal acid ester or metal hydroxide colloidmay be used as the bonding material.

In the above embodiment, the optical elements are bonded together.Alternatively, an optical element and a metal element may be bonded bythe present method.

The optical elements to be bonded by the present method include anyelement which condenses, reflects, refracts or interferes light, such aslens, prism, mirror or grating. Accordingly, the optical elementsmanufactured by the present method include those having the bondingprocess in their manufacturing process.

As described above, the present manufacturing method which uses themetal alcoholate as the bonding material for the optical elementprovides a high bonding strength, assures matching of the refractiveindices of the bonding layer and the substrate, reduces the absorptionof light by the bonding layer and prevents the reduction of thetransmissivity. Accordingly, the present invention can be used veryeffectively in the manufacture of a variety of optical products.

FIG. 2 shows a prism type polarized beam splitter, which comprises aprism 21 having a polarized beam splitter film 23 formed thereon, aprism 22 and a hydrolysis product 24 of Si-alcoholate which bonds theprisms 21 and 22.

The prisms 21 and 22 are made of synthesized silica the polarized beamsplitter film 23 formed on the prism 21 is a dielectric multi-layer filmwhich is formed by vacuum deposition, sputtering or ion plating. Aspectrograph of the polarized beam splitter is shown in FIG. 3, in whichnumeral 5 represents a reflection factor of a P polarization componentand numeral 6 represents a reflection, factor of an S polarizationcomponent. The polarized beam splitter is designed for KrF Xma laser.

In the present embodiment, Si-alcoholate is again used to bond theprisms 21 and 22 of the polarized beam splitter. When Si-alcoholate ishydrolyzed, it changes to vitreous SiO₂ and presents bonding ability anddoes not essentially absorb a light in the ultraviolet range. Thus, itmay be used as the bonding material. Since the hydrolysis product 24 ofSi alcoholate and the silica glass of the prisms 21 and 22 are of thesame composition, the refractive indices match, the affinity is high,and high bonding strength is provided.

Condition and catalyst for the hydrolysis of Si-alcoholate are notrestricted and the hydrolysis may be carried out in a usual manner.

After the hydrolysis, alcohol or ester solvent residues such as lowboiling point alcohol or ester (for example ethyl alcohol or estersulfate, volatilizes after the bonding. In order to positively removeit, the assembly may be heated or vacuumed. If there is foreign materialsuch as dust or impurity on the bonding surface, the bonding strength islowered or it may be damaged by the laser. Accordingly, it is necessaryto fully clean the bonding surface before the bonding process and filterthe bonding material to remove the impurities. A clean room ispreferable for a work environment.

In order to bond the prisms 21 and 22, the hydrolysis product 24 ofSi-alcoholate is coated to the bonding surfaces of the lenses. This maybe done by a conventional method such as dropping the hydrolysis product24 onto the bonding surfaces and bonding them together. When it isdesired to form a thin bonding layer such as 1 μm, the following methodis preferable. The lenses are contacted together, the hydrolysis product24 of Si-alcoholate is injected into a clearance therebetween by aninjector so that the hydrolysis product 24 is spread over the entirebonding surfaces of the lenses by a capillarity. In this method, inorder to spread the hydrolysis product of Si-alcoholate over the bondingsurfaces and control the rate of formation of the film and the filmthickness, it is necessary that the hydrolysis product of Si-alcoholatehas an appropriate viscosity. This is attained by solving the hydrolysisproduct of metal alcoholate into a selected solution. The solution maybe a high boiling point alcohol such as butyl alcohol, or ester.

By heating Si-alcoholate after the hydrolysis, it is dehydrated andpolymerized and changes to an amorphous SiO₂ film and approaches to thematerial of the optical element. In the present invention, particularlyin the present embodiment, the bonding layer without heating exhibitsthe same optical property as that obtained by the heating and has apractically sufficiently high bonding ability. Accordingly, heating isnot necessary.

When the present invention is applied to the manufacture ofGlan-Thomson, Glan-Tiller, or Wallstone prism and the components thereofare bonded by the hydrolysis product of Si-alcoholate, a prism which canbe used in a shorter wavelength range than was usable by the prior artprism can be provided.

In the manufacturing method described above, when the optical element ismanufactured by bonding the element primarily made of SiO₂ and theelement having a metal or dielectric thin film formed thereon, asufficiently high bonding strength may not be attained in a certain casedepending on the composition of the thin film serving as the bondingsurface and a difference between surface roughnesses of the bondingsurfaces, an embodiment shown below improves such a deficiency. WhenSi-alcoholate is used as the bonding material in the manufacture of theoptical element, an SiO₂ layer is formed on at least one of the pair ofbonding surfaces so that the bonding strength of Si-alcoholate isenhanced independently from the surface condition of the bondingsurfaces, without affecting the optical property of the optical element.

FIG. 4 shows a prism type polarized beam splitter for the KrF Xma laser.It comprises a prism 21 having a multi-layer polarized beam splitterfilm 23 formed thereon, a prism 22 and bonding material which bonds theprisms 21 and 22. When the polarized beam splitter film 23 has a layerstructure shown in Table 1, that is, a high refractive index materialZrO₂ and a low refractive index material SiO₂ are alternately formedwith the outermost layer being the ZrO₂ layer, the bonding strength ofthe hydrolysis product 24 of Si-alcoholate which bonds the prism 21having the polarized beam splitter film 23 formed thereon and the prism22 may not be sufficiently high. When the polarized beam splitter film23 has the SiO₂ layer as the outermost layer 30 as shown in Table 2, thebonding strength for the prisms by the hydrolysis product ofSi-alcoholate is significantly improved.

                  TABLE 1                                                         ______________________________________                                                 Refractive Optical Film                                                       Index      Thickness Film Material                                   ______________________________________                                        Substrate                                                                              1.51       --        (Synthesized Silica)                            Layer 1  2.12        80 (nm)  ZrO.sub.2                                       2        1.53       100.2     SiO.sub.2                                       3        2.12        80       ZrO.sub.2                                       4        1.53       100.2     SiO.sub.2                                       5        2.12        80       ZrO.sub.2                                       6        1.53       100.2     SiO.sub.2                                       7        2.12        80       ZrO.sub.2                                       8        1.53       100.2     SiO.sub.2                                       9        2.12        80       ZrO.sub.2                                       10       1.53       100.2     SiO.sub.2                                       11       2.12        80       ZrO.sub.2                                       12       1.53       100.2     SiO.sub.2                                       13       2.12        80       ZrO.sub.2                                       14       1.53       100.2     SiO.sub.2                                       15       2.12        80       ZrO.sub.2                                       Bonding  1.51       --        Si-alcoholate                                   Layer                                                                         Substrate                                                                              1.51       --        (Synthesized Silica)                            ______________________________________                                         Note: Refractive index is for wavelength of 248 nm.                      

                  TABLE 2                                                         ______________________________________                                                 Refractive Optical Film                                                       Index      Thickness Film Material                                   ______________________________________                                        Substrate                                                                              1.51       --        (Synthesized Silica)                            Layer 1  2.12        80 (nm)  ZrO.sub.2                                       2        1.53       100.2     SiO.sub.2                                       3        2.12        80       ZrO.sub.2                                       4        1.53       100.2     SiO.sub.2                                       5        2.12        80       ZrO.sub.2                                       6        1.53       100.2     SiO.sub.2                                       7        2.12        80       ZrO.sub.2                                       8        1.53       100.2     SiO.sub.2                                       9        2.12        80       ZrO.sub.2                                       10       1.53       100.2     SiO.sub.2                                       11       2.12        80       ZrO.sub.2                                       12       1.53       100.2     SiO.sub.2                                       13       2.12        80       ZrO.sub.2                                       14       1.53       100.2     SiO.sub.2                                       15       2.12        80       ZrO.sub.2                                       16       1.53       200.4     SiO.sub.2                                       Bonding  1.51       --        Si-alcoholate                                   Layer                                                                         Substrate                                                                              1.51       --        (Synthesized Silica)                            ______________________________________                                         Note: Refractive index is for wavelength of 248 nm.                      

The enhancement of the bonding strength by the present embodiment is forthe following reason. The hydrolysis product of Si-alcoholate used asthe bonding material is dehydrated and polymerized and changes to a SiO₂amorphous film, which presents a bonding ability. The composition of thebonding surface of the prism 22 made of synthesized silica hasessentially the same composition as the amorphous film. On the otherhand, the bonding surface of the prism 21 having the polarized beamsplitter film 23 formed thereon is ZrO₂ in the layer structure shown inTable 1. It is an oxide but the material is different. Accordingly,affinity is low. When the surface of ZrO₂ is rough, the affinity isfurther lowered and the bonding strength is considerably lowered. In thelayer structure shown in Table 2 in accordance with the presentinvention, the outermost layer 30 of the prism 21 having the polarizedbeam splitter film 23 formed thereon is SiO₂. Thus, the affinity to thebonding layer is significantly enhanced. As a result, high bondingstrength is maintained even if the surface roughness of the bondingsurface increases.

Spectrographs of the polarized beam splitters having the layerstructures of Tables 1 and 2 are shown in FIGS. 5 and 6, respectively. Acurve 5 represents a reflection factor of P polarization component, anda curve 6 shows a reflection factor of S polarization component. WhenSiO₂ is added, there is no change in the spectrograph and the Spolarization component and P polarization component at KrF Xma laser(λ=248 nm) are fully separated.

In the present method, the SiO₂ layer may be formed by vacuumdeposition, sputtering or ion plating. The thickness of the SiO₂ layeris preferably m/2 (m=1, 2, 3, . . . ) of a design reference wavelengthof the optical element while taking the optical characteristic of theoptical element into account.

The method for manufacturing the prism type polarized beam splittershown in FIG. 4 is same as that of the prism type polarized beamsplitter shown in FIG. 2, except that an SiO₂ layer is used as theoutermost layer 30 of the polarized beam splitter film 23.

Accordingly, the manufacturing method of the present embodiment can beapplied to manufacture the optical element which is manufactured bybonding optical elements having functions of condensing, reflecting,refracting or interfering the light, so long as the function of theproduct is within the practical acceptable range. For example, anoptical element having a metal film formed thereon such as a metalhalf-mirror or an optical element having no dielectric film or metalfilm formed thereon (for example, lens or prism primarily made of oxideother than SiO₂) may be used.

In the present invention, the SiO₂ layers may be formed on both bondingsurfaces as required.

As described above, in accordance with the present method formanufacturing the optical element, the SiO₂ layer is formed on thesurface of the optical element which serves as the bonding surface, andSi-alcoholate is used as the bonding material. Accordingly, the bondingstrength between the elements is significantly enhanced.

FIG. 8 shows a flow chart of the manufacturing method of the presentinvention for the prism type polarized beam splitters shown in FIGS. 2and 4.

In the manufacture of the bonded lens shown in FIG. 1, the presentmethod may be used. Namely, the SiO₂ film is formed on the bondingsurface of the fluorite lens 2 and then the silica lens 1 and thefluorite lens 2 are bonded by the hydrolysis product of Si-alcoholate.Thus, the bonding strength is further enhanced.

Other embodiment of the present invention is described. An opticalelement manufactured in the present method is the prism type polarizedbeam splitter shown in FIG. 2.

As described above, the polarized beam splitter of this type comprisesthe prism 21 having a multi-layer polarized beam splitter film 23 formedthereon and the prism 22, bonded together by the bonding material (seeFIG. 2).

In the present embodiment, in order to bond the two prisms, a condensateof ethyl silicate Si_(n) O_(n-1) (OC₂ H₅) (n=5) which is Si-alcoholateand Ti-isoproxide which is Ti-alcoholate are prepared.

Mixture of those two alcoholates is hydrolyzed. The product exhibits abonding ability and a refractive index thereof varies between n=1.45˜2.2by changing a mixing ratio of the alcoholates. It is necessary todetermine the mixing ratio of the alcoholates so that the hydrolysisproduct 24 of the alcoholate mixture has substantially the samerefractive index as the prisms 21 and 24 to be bonded. The prisms usedin the present embodiment are BK-7 which have a refractive index of1.52. Thus, the mixing ratio (mole ratio) is selected to beSi-alcoholate 4 to Ti-isoproxide 1 so that the refractive index of thebonding material is substantially equal to 1.52.

The alcoholates mixed at the above ratio are hydrolyzed and the twoprisms 21 and 22 having the polarization film formed on one of them arebonded by the hydrolysis product. In this manner, the polarized beamsplitter shown in FIG. 2 is manufactured.

After the hydrolysis, alcohol or ester solvent residues but low boilingpoint alcohol or ester (for example, ethyl alcohol or ester sulfatevolatilizes after the bonding. In order to positively remove it, theassembly may be heated or vacuumed. If there is foreign material such asdust or impurity on the bonding surface, the bonding strength is loweredor it may be damaged by the laser. Accordingly, it is necessary to fullyclean the bonding surface before the bonding process and filter thebonding material to remove the impurities. A clean room is preferablefor a work environment.

In order to bond the prisms 21 and 22, the hydrolysis product 24 ofSi-alcoholate is coated to the bonding surfaces of the lenses. This maybe done by a conventional method such as dropping the hydrolysis product24 onto the bonding surfaces and bonding them together. When it isdesired to form a thin bonding layer such as 1 μm, the following methodis preferable. The lenses are contacted together, the hydrolysis product24 of Si-alcoholate is injected into a clearance therebetween by aninjector so that the hydrolysis product 24 is spread over the entirebonding surfaces of the lenses by a capillarity. In this method, inorder to spread the hydrolysis product of Si-alcoholate over the bondingsurfaces and control the rate of formation of the film and the filmthickness, it is necessary that the hydrolysis product of Si-alcoholatehas an appropriate viscosity. This is attained by solving the hydrolysisproduct of metal alcoholate into a selected solution. The solution maybe a high boiling point alcohol such as butyl alcohol, or ester.

By heating metal alcoholate after the hydrolysis, it is dehydrated andpolymerized and changes to an amorphous metal oxide film and approachesto the material of the optical element. In the present invention,particularly in the present embodiment, the bonding layer withoutheating exhibits the same optical property as that obtained by theheating and has a practical sufficiently high bonding ability.Accordingly, heating is not necessary.

In the present invention, the alcoholates are not limited toSi-alcoholate and Ti-alcoholate but hydrolysis product of a mixture ofany two or more metal alcoholates may be used as the bonding material.The metal alcoholate which can be used in the present invention isrepresented by M(OR)_(n) for single alcoholate, where M is a metal (Si,Ti, Al, Zn, Ta, etc.) and (OR)_(n) is alcohoxyl radical. For mixed metalalcoholate, for example, Si and M(:Ti, Al, Zr) at a mixing ratio of 4/1,it is represented by (Si_(4n/5) M_(n/5))O_(n-1) (OR)2n+2. Specifically,Si(O•C₂ H₅)₄ silicon tetraethoxide, Al(O•isoC₃ H₇)₃ aluminumisopropoxyde, or Ti(O•isoC₃ H₇)₄ titanium isopropoxide may be used.

As described in Applied Optics vol. 20, No. 1, pages 40˜47 by Roger W.Phillips and Jerry W. Doodds, the refractive index of the mixedalcoholate film of the metal alcoholates is variable between 1.45 and2.0 for the hydrolysis product of Si and Zr mixed alcoholate, andbetween 1.45 and 1.6 for the hydrolysis product of Si and Al mixedalcoholate.

The optical element to be bonded by the present method includes anyelement which condenses, reflects, refracts or interferes light. Itincludes lens and prism as well as mirror and grating. Accordingly, theoptical element manufactured by the present invention includes thosehaving a bonding process in the manufacturing process. Preferably, thematerial of the optical element used in the present method primarilyconsists of oxide.

The present invention is applicable to manufacture not only the opticalelement having elements bonded together but also an optical elementcomprising an optical element and a metal element.

As described above, in accordance with the present invention, thehydrolysis product of the mixed metal alcoholate which allows control ofthe refractive index over a wide range (for example 1.45˜2.20) is usedas the bonding material. Accordingly, the refractive indices of thebonding layer and the substrate can be readily matched irrespective ofthe type of substrate, the optical design is facilitated and opticalproperty of the optical element is improved. Further, the material ofthe optical element can be freely selected.

I claim:
 1. A method for manufacturing an optical device fortransmitting light in an ultraviolet range comprising the steps of:(a)selecting a first optical component made of silica; (b) selecting asecond optical component made of a material other than a silica, saidmaterial being transparent against light in an ultraviolet range; (c)cleaning surfaces of said first optical component and said secondoptical component of said device and forming a silica film on a bondingsurface of said second optical component; (d) providing a hydrolysisproduct of a silicon alcoholate, said hydrolysis product comprising (i)an amorphous silicon oxide and (ii) a volatilizable liquid; (e)introducing said hydrolysis product of the silicon alcoholate bycapillary action in a space between said first optical component and thesilica film on said second optical component; and (f) contacting saidfirst optical component and the silica film on said second opticalcomponent with said hydrolysis product of the silicon alcoholate in thespace between said first optical component and the silica film on saidsecond optical component, thereby joining said first optical componentand said second optical component by forming a bond of said amorphoussilicon oxide between said first optical component and said secondoptical component and volatilizing said volatilizable liquid.
 2. Amethod of manufacturing an optical device according to claim 1, whereinsaid second optical component is made of fluorite.
 3. A method formanufacturing an optical device for transmitting light in an ultravioletrange comprising the steps of:(a) selecting a first lens made of silica;(b) selecting a second lens made of a material other than a silica, saidmaterial being transparent against light in an ultraviolet range; (c)cleaning surfaces of said first lens and said second lens of said deviceand forming a silica film on a bonding surface of said second lens; (d)providing a hydrolysis product of a silicon alcoholate, said hydrolysisproduct comprising (i) an amorphous silicon oxide and (ii) avolatilizable liquid; (e) introducing said hydrolysis product of thesilicon alcoholate by capillary action in a space between said firstlens and the silica film on said second lens; and (f) contacting saidfirst lens and the silica film on said second lens with said hydrolysisproduct of the silicon alcoholate in said space between said first lensand the silica film on said second lens thereby joining said first lensand said second lens by forming a bond of said amorphous silicon oxidebetween said first lens and said second lens and volatilizing saidvolatilizable liquid.
 4. A method for manufacturing an optical deviceaccording to claim 3, wherein said second lens is made of fluorite.
 5. Amethod for manufacturing an optical device for transmitting light in anultraviolet range comprising the steps of:(a) selecting a first opticalcomponent made of silica; (b) selecting a second optical component madeof a material other than a silica, said material being transparentagainst light in an ultraviolet range; (c) cleaning surfaces of saidfirst optical component and said second optical component of said deviceand forming a silica film on a bonding surface of said second opticalcomponent; (d) providing a hydrolysis product of a silicon alcoholate,said hydrolysis product comprising (i) an amorphous silicon oxide and(ii) a volatilizable liquid; (e) introducing said hydrolysis product ofthe silicon alcoholate in a space between said first optical componentand the silica film on said second optical component; and (f) contactingsaid first optical component and the silica film on said second opticalcomponent with said hydrolysis product of the silicon alcoholate in thespace between said first optical component and the silica film on saidsecond optical component, thereby joining said first optical componentand said second optical component by forming a bond of said amorphoussilicon oxide between said first optical component and said secondoptical component and volatilizing said volatilizable liquid.
 6. Amethod of manufacturing an optical device according to claim 5, whereinsaid second optical component is made of fluorite.
 7. A method formanufacturing an optical device for transmitting light in an ultravioletrange comprising the steps of:(a) selecting a first lens made of silica;(b) selecting a second lens made of a material other than a silica, saidmaterial being transparent against light in an ultraviolet range; (c)cleaning surfaces of said first lens and said second lens of said deviceand forming a silica film on a bonding surface of said second lens; (d)providing a hydrolysis product of a silicon alcoholate, said hydrolysisproduct comprising (i) an amorphous silicon oxide and (ii) avolatilizable liquid; (e) introducing said hydrolysis product of thesilicon alcoholate in a space between said first lens and the silicafilm on said second lens; and (f) contacting said first lens and thesilica film on said second lens with said hydrolysis product of thesilicon alcoholate in said space between said first lens and the silicafilm on said second lens, thereby joining said first lens and saidsecond lens by forming a bond of said amorphous silicon oxide betweensaid first lens and said second lens and volatilizing said volatilizableliquid.
 8. A method of manufacturing an optical device according toclaim 7, wherein said second lens is made of fluorite.